IC 


8938 



Bureau of Mines Information Circular/1983 



New Developments in Personal 
Lighting Systems for Miners 

By William H. Lewis and Elio Ferreira 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 8938 



New Developments in Personal 
Lighting Systems for Miners 

By William) H. Lewis and Elio Ferreira 




UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 







This publication has been cataloged as follows: 



Lewis, W. H. (William H.) 

New developments in personal lighting systems for miners. 

(Information circular / United States Department of the Interior, Bu- 
reau of Mines ; 8938) 

Supt. of Docs, no.: I 28.27:8938. 

1. Safety-lamp. 2. Nickel-cadmium batteries. 3. Mine lighting- 
Equipment and supplies. I. Ferreira, Elio. II. United States. Bureau 
of Mines. III. Title. IV. Series: Information circular (United States. 
Bureau of Mines) ; 8938. 



IE205tIM^' [TN307] 622s [622'. 473] 



83-600085 



c 



^! 



^ CONTENTS 

Page 

Abstract 1 

:<^ Introduction 2 

^Electrochemical design , 3 

,,^ Roll-bonded electrode process 4 

>v Positive electrode fabrication 4 

^ Negative electrode fabrication 4 

-^ Electrolyte 4 

Cell design 5 

Separator 5 

Battery construction 6 

Cycle testing 9 

Conclusions , 10 

ILLUSTRATIONS 

1. Conventional lead-acid battery and prototype nickel-cadmium battery 2 

2. Roll-bonded nickel-cadmium cell with separators 6 

3 . Complete cell assembly 6 

4. Molded battery case 7 

5. Fill port-level indicator 7 

6. Fill port-level indicator installed in case 7 

7. Terminal cover attached to battery case 8 

8. Outer battery cover 8 

9. Lamp cord wiring arrangement and intercell connections 9 

10. Typical discharge curve of nickel-cadmium caplamp battery 10 

11. Battery-end cutoff voltage versus time 10 

TABLE 

1 . Comparative battery specifications 3 



do 



^ 



'^ 



^ 



UNIT 


OF MEASURE ABBREVIATIONS 


USED IN 


THIS 


REPORT 


A 


ampere 


min 




minute 


A»h 


ampere hour 


ym 




micrometer 


g 


gram 


pet 




percent 


h 


hour 


s 




second 


in 


inch 


V 




volt 


in3 


cubic inch 


W'h 




watt hour 


in'lb 


inch pound 


yr 




year 


lb 


pound 









NEW DEVELOPMENTS IN PERSONAL LIGHTING SYSTEMS FOR MINERS 

By William H. Lewis ^ and Elio Ferreira^ 



ABSTRACT 

Energy Research Corp., under contract to the Bureau of Mines, has 
developed a new miners' caplamp battery. The new battery is based on 
nickel-cadmium technology and offers significant improvements in per- 
formance with reduced size and weight when compared to the conventional 
lead-acid battery presently in use. This report describes the design 
and fabrication of the nickel-cadmium battery, which utilizes a roll- 
bonded electrode structure. The final battery design has a 15-A*h 
capacity in a 2-1/2-lb package, which is over 2 lb lighter than the 
present lead-acid caplamp battery. 

'Electrical engineer, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
^Project engineer. Energy Research Corp., Danbury, CT. 



INTRODUCTION 



The present-day miner's caplamp and 
battery system has been a highly reliable 
and indispensable aid to miners for many 
years and has undergone few changes since 
its general acceptance in the 1930' s. 



Recent developments in 
ogy, however, have made 
ments possible. 



battery technol- 
several improve- 



Over the past 3 yr, Energy Research 
Corp., under contract to the Bureau of 
Mines , has been developing a new caplamp 
and battery system. The new battery is 
based on nickel-cadmium technology and 
features significant improvements in per- 
formance when compared to the conven- 
tional lead-acid battery presently in use 
(fig. 1). 

Among the more significant improvements 
are a 48-pct reduction in battery weight 



and a 15-pct reduction in battery volume. 
The over-2-lb weight reduction should be 
an attractive feature to miners , who must 
carry the battery while performing their 
work. Battery capacity has been in- 
creased from 12 to 15 A*h and will pro- 
vide a greater margin of safety and cap- 
lamp burning time that may be required 
in emergency situations. Charging cycle 
life has been also increased, and al- 
though testing has not been completed, 
it is expected to be in the 1,000-cycle 
range. This will extend the usable life 
of the battery to approximately 2-1/2 
times that of the present lead-acid bat- 
tery, providing 3 to 4 yr of normal use. 
The extended battery life should more 
than offset the higher cost of the 
nickel-cadmium system. Table 1 compares 
the specifications of the old and new 
batteries. 




FIGURE 1. - Conventional lead-acid battery (left) and prototype nickeUcadmium battery (right). 



TABLE 1. - Comparative battery specifications 



Specification 



Nickel-cadmium 
(prototype) 



Lead-acid 
(typical) 



Weight lb. . 

Voltage (average) V. . 

Capacity A*h. . 

Ene rgy W • h . . 

Energy density W*h/lb.. 

Size in. . 

Volume in^ . . 

Energy density W*h/in^ . . 

Charging cycle life cycles.. 

Cost 




1.64 X 4.90 X 



4.66 

3.7 

12 

44 

9.5 

6.65 

53.4 

0.82 

<400 

$30 



^Cost is a function of production volume. The projected 
is based on a production volume of 20,000 units per year. 

ELECTROCHEMICAL DESIGN 



cost figure 



Nickel-cadmium batteries were first 
developed in Europe and have been in use 
for more than 60 yr. The basic nickel- 
cadmium cell is a rechargeable system 
which consists of a combination of active 
materials that can be electrolytically 
oxidized and reduced repeatedly. The 
overall chemical reaction of the system 
can be considered as follows: 



Cd + 2NiOOH + oHoO 



(CHARGED) 



2"2^ 



^=^ Cd(0H)2 + 2Ni(0H)2. 
KOH (DISCHARGED) 



In a charged condition, the system con- 
sists of a positive electrode (nickelic 
hydroxide) and a negative electrode (me- 
tallic cadmium). Potassium hydroxide is 
used as an electrolyte. In an uncharged 
condition, the positive electrode be- 
comes reduced to nickelous hydroxide and 
the negative electrode oxidized to cad- 
mium hydroxide. The oxidation of the 
negative electrode occurring simulta- 
neously with the reduction of the posi- 
tive electrode generates electric power. 
In a rechargeable battery, such as the 
nickel-cadmium system, both electrode re- 
actions are reversible and by supplying 
an electric current from an external 
source, the reactions can be driven 
backwards and in effect recharge the 
electrodes. 



Over the years many techniques and pro- 
cesses have been developed for economi- 
cal manufacture of the nickel-cadmium 
electrode structures, and basically two 
types have evolved: sintered plate elec- 
trodes, and nonsintered electrodes. 

The following discussion will focus on 
the development of the roll-bonded (non- 
sintered type) nickel-cadmium electrodes 
that are used in the design of the new 
caplamp battery. The term "roll-bonded 
electrode" refers to electrodes fabri- 
cated by forming a conductive mix of 
Ni(0H)2 (nickel hydroxide) or CdO (cad- 
mium oxide) and Teflon^ into a bonded 
structure by rolling in a calendaring 
mill. The steps comprising the manufac- 
ture of roll-bonded electrodes are all 
semicontinuous or are automated to a 
greater degree than those for sintered 
electrodes. Moreover, the nonsintered, 
or roll-bonded, process offers the fol- 
lowing advantages: 

• Lower nickel requirements 

• Lower material cost 

^Reference to specific products does 
not imply endorsement by the Bureau of 
Mines. 



• Lower labor cost 

• Lower capital equipment cost 

• Lighter weight 

• Lower pollution stream 

• Lower process energy requirements 

ROLL-BONDED ELECTRODE PROCESS 

The processing steps in the manufacture 
of the nickel-cadmium electrodes consist 
of similar operations. The discussion 
begins with the process for fabricating 
nickel electrodes. 

Positive Electrode Fabrication 

Nickel hydroxide is prepared by precip- 
itation from NiSO^ (nickel sulfate) solu- 
tion containing a small percentage of 
CoSO^ (cobalt sulfate); Co(0H)2 (cobalt 
hydroxide) is coprecipitated with Ni(0H)2 
(nickel hydroxide). The Co(0H)2 is com- 
bined with the active material to give 
good charge efficiency and capacity re- 
tention to the electrode. The precipi- 
tate is washed to remove K2S04 (potassium 
sulfate) and KOH (potassium hydroxide) 
and dried. It has been found that the 
particle size of the Ni(0H)2 powder is of 
primary importance in determining the 
utilization and voltage characteristics 
of the finished electrodes. 

In the next step, Ni(0H)2/Co(0H)2 is 
blended with graphite, Teflon, and an or- 
ganic lubricant. The mixture of nickel 
hydroxide, graphite, and Teflon is 
kneaded to fibrillate the Teflon, which 
acts as a binder or matrix for containing 
the active materials. Specially selected 
graphites are used as the conductive dil- 
uent to impart electrical conductivity to 
the Ni(0H)2, which is otherwise an insu- 
lator. The organic lubricant is added to 
act as a rolling and extrusion aid to 
help "work" the mixture to the proper 
consistency. 

At this point, the doughlike material 
is sent through a rolling mill which 



forms it into sheets and calendars it to 
the proper thickness. The electrode 
sheets are then dried to remove the 
solvent and cut to size with a shear. 
The electrode strip at this point is 
self-supporting, flexible, and mechani- 
cally rugged, and can be easily handled 
for subsequent manufacturing. The nature 
of the roll-bonded process allows manu- 
facture of electrodes with variations in 
thickness from 0.005 in to more than 
0.25 in. This permits a greater latitude 
in cell design than is attainable with 
the sintered electiode process. 

The final steps in the process are the 
fabrication of the current collector and 
its lamination to the positive active 
material. The current collector consists 
of a nickel foil, which is cut to size 
and perforated. 

Negative Electrode Fabrication 

The roll-bonded cadmium electrode con- 
sists of a mixture of CdO (cadmium ox- 
ide) , carbonyl nickel powder, and Tef- 
lon, which is processed as previously 
described and laminated to a perforated 
nickel foil current collector. 

To obtain maximum utilization of active 
material, the particle size of cadmium 
oxide must be between 2 and 6 urn. For- 
tunately, commercially available CdO pow- 
der satisfies this requirement. Carbonyl 
nickel powder is added to improve the 
wettability and conductivity. This 
provides good capacity, especially during 
early formation cycling, and prevents re- 
crystallization of the active material. 

ELECTROLYTE 

The electrolyte used is a solution con- 
taining 35 pet KOH (potassium hydroxide) , 
1 pet LiOH (lithium hydroxide) , and other 
additives. The use of 35 pet KOH is 
based on the optimum low-temperature 
characteristics of the electrolyte con- 
centration; also its conductivity is 
optimum at this percentage. Lithium 
hydroxide is added to improve cycle 
capacity stability. 



CELL DESIGN 

The Code of Federal Regulations, Min- 
erals Resources, CFR 30, Part 19.9 (a) 
specifies that "Permissible electric cap- 
lamps shall burn for at least 10 con- 
secutive hours on one charge of the bat- 
tery and shall give during that period 
a mean candlepower of light beam of not 
less than 1." 

Based on the above specifications and 
targeted physical dimensions, a cell de- 
sign was developed with a nominal capac- 
ity of 15 A*h and an output voltage of 
3.6 V. 

The calculations used in designing the 
cell are based on previous experimental 



tests on similar cells. Faradaic cal- 
culations show that it takes 3.65 g 
of nickel hydrate [Ni(0H)2 • 1/3 H2O] to 
produce 1 A'h of capacity. 

Experimentally, it has been found that, 
using a 10-pct overcharge, the conserva- 
tive utilization of nickel hydrate is 
80 pet and that of CdO is 60 pet of theo- 
retical. Slight variations in these fig- 
ures can be obtained as the number of 
electrodes, amount of graphite, and dis- 
charge current density are varied. Based 
on the amount of active material (nickel 
hydroxide) on the positive electrode of 
11.3 g, the nominal capacity of the cell 
can be calculated as follows; 



Nominal capacity = 

The basic cell consists of six positive 
electrodes, five full-thickness negative 
plates, and two half-thickness negative 
plates. The positive mix formula has 
been optimized for the current drain of 
the bulb. In this design the low dis- 
charge current density allows the graph- 
ite content to be reduced, thereby allow- 
ing more hydrate to be used. The optimum 
particle size of the graphite was deter- 
mined experimentally and is a compromise 
among several factors. First, if the 
particle size is too large, the graphite 
will not blend homogeneously with the 
nickel hydrate and Teflon and will yield 
a poor physical mix that will affect the 
performance of the electrode. Second, if 
the particle size is too fine, the bulk 
density decreases, making it difficult to 
obtain the proper capacity density 
(A-h/in3). 

The quantity of graphite is based on 
several factors: Owing to the low cur- 
rent density of 1.3 A, this being the 
rate of discharge with a 3.6-V caplamp 
bulb, it is not necessary to increase the 



11.3 g X 6 plates/cell x 0.80 utilization 



3.65 g/A-h 



= 15 A-h. 



amount of graphite, where very high con- 
ductivity would otherwise be required. 
It has been shown experimentally that 
when the graphite content is below the 
design value, conductivity is much poor- 
er, impairing the performance of the 
electrode and reducing its capacity. 

SEPARATOR 

The separator system is composed of one 
5-mil Pellon (nonwoven polyamide) bag 
heat-sealed around the positive elec- 
trode, followed by a layer of U-wrapped 
Celgard K 306 microporous polypropylene 
film. The separators are important in 
vented nickel-cadmium cells in preventing 
cadmium shorts from penetrating to the 
positive during extended cycling. The 
Celgard K 306 film has shown good long- 
terra oxidation resistance during acceler- 
ated chemical testing and can be commer- 
cially produced in quantities for this 
type of battery. Figure 2 shows the as- 
sembled nickel-cadmium cell with sepa- 
rators in place. 







FIGURE 2. = RolUbonded nickel-cadmium cell 
with separators. 



FIGURE 3. = Complete cell assembly. 



BATTERY CONSTRUCTION 



Based on capacity requirements (15 
A*h) , the final battery size was estab- 
lished at 1.77 In deep by 3.92 In wide by 
6.65 In high. The battery consists of 
three cells connected in series. Each 
cell Is composed of six positive elec- 
trodes, five full-thickness negative 
plates, and two half -thickness negative 
plates assembled to a terminal cover as 
shown in figure 3. Each cell is termi- 
nated with two threaded studs, attached 
to the terminal cover with nuts , and 
torqued to 15 in -lb. 0-rlng seals are 
used between the terminals and cover to 
prevent leakage of the electrolyte. 



The battery case is molded of Polysul- 
fone and is compartmented for each cell 
assembly (fig. 4). Polysulfone was chos- 
en as the molding material because of its 
high impact strength and good chemical 
resistance. Chemically, it is stable in 
KOH solutions and highly resistant to 
aqueous mineral acids and salt solutions; 
its resistance to detergents and hydro- 
carbon oil is good even at elevated 
temperatures and under moderate levels of 
stress. Another important property of 
Polysulfone is that it can be easily 
solvent-bonded to itself by using methyl- 
ene chloride. 





FIGURE 4. - Molded battery case. 



FIGURE 5. - Fill port-level indicator. 



Based on the MSHA (Mine Safety and 
Health Administration) drop test require- 
ments and application of the battery, the 
case and cover were designed with rein- 
forced corners and a wall thickness of at 
least 1/8 in. The battery case is de- 
signed with three viewports which are 
fitted with Polysulfone fill ports-level 
indicators. These devices facilitate 
maintenance of the battery by permitting 
the user to visually check and adjust the 
electrolyte level (fig. 5). 



' 1 



^ ^ 



ft 



The fill port-level indicator is de- 
signed with a baffle arrangement to pre- 
vent electrolyte spillage, even though 
the battery is positioned upside down or 
sideways. Sufficient headroom is also 
provided in the cell to allow operation 
in any position without spilling the 
electrolyte (fig. 6). 

The primary seal between the battery 
case and terminal cover is attained by 
solvent-bonding with methylene chloride, 
followed by a secondary epoxy seal which 
is poured around the well provided at the 
top edge of the terminal cover (fig. 7). 

The battery is provided with an outer 
cover constructed of 0.025-in-thick 
stainless steel. The cover is attached 
to the battery with two L-shaped brackets 
and two No. 6-32 screws (fig. 8). 

Battery charging is accomplished 
through the lamp cord, which fits into 
the outer cover by means of a rubber boot 



j 

1 




L 


J, 



FIGURE 6. - Fill port-level indicator in- 
stalled in case. 




FIGURE 7. - Terminal cover attached to battery case. 




FIGURE 8. - Outer battery cover. 




FIGURE 9. - Lamp cord wiring arrangement and intercell connections. 



and bushing. The connections between the 
cord and terminal studs are made through 
lugs and secured with nuts. Six termi- 
nals are connected in series through an 
intercell connector and a thermoswitch 
(fig. 9). 

The thermoswitch serves not only as an 
intercell connector but also as a safety 



switch. Several types of thermoswitches 
were tested for their trip and reset 
temperature and time. The thermoswitch 
selected for this design has a trip tem- 
perature of approximately 120° C at a 
trip current of 8.1 A. Its reset temper- 
ature is approximately 78° C. Trip and 
reset times are 2 and 3 s, respectively. 



CYCLE TESTING 



Several cell des 
factured utilizing 
ments developed dur 
of these improveme 
least 360 cycles, 
discharge period 
a charge period of 
a typical plot 
as a function of 
conditions. 



igns have been manu- 

the design improve- 

ing this study. Some 

nts have produced at 

each cycle being a 

of 10 h followed by 

14 h. Figure 10 shows 

of battery voltage 

time during discharge 



When studing the cycle capacity of 
the battery, two major factors were con- 
sidered: (1) the number of times that 
the battery can be cycled (discharged 
and charged) and (2) the variation of 
battery-end cutoff voltage (voltage of 
the 10th h of discharge) with cycling. 
The battery-end cutoff voltage is impor- 
tant, because it determines the amount of 
light output from the caplamp. Federal 



10 



4.00 




FIGURE 10. - Typical discharge curve of nickel-cadmium capiomp battery. 



>3.6 




100 150 200 250 

NUMBER OF CYCLES, lO-h discharge 

FIGURE 11. - Battery-end cutoff voltage versus time. 



300 



350 



regulations require the battery to have 
sufficient capacity to maintain a beam 
candle power of not less than 1 during 
10 h of continuous use. It has been de- 
termined experimentally that the voltage 
to the caplamp must be at least 3 V to 
meet these requirements. Since the 
battery-end cutoff voltage gradually de- 
creases as the battery is cycled, eventu- 
ally the voltage will fall below the re- 
quired limits. Figure 11 is a plot of 



the battery-end cutoff voltage as a func- 
tion of the number of cycles. It can be 
seen from the plot that the voltage after 
360 cycles has fallen to approximately 
3.4 V, which is more than adequate to 
meet the candlepower requirements. Based 
on previous experience with similar types 
of batteries and data on the present de- 
sign, it is expected that the life will 
be in the 1,000-cycle range. 



CONCLUSIONS 



The nickel-cadmium battery developed 
during this study offers great promise 
to the mining industry as a long-life, 
lightweight battery for caplamp appli- 
cations. The reduction of over 2 lb 
of weight when compared to the present 



lead-acid battery and increased perform- 
ance should be attractive features to 
mining personnel. The projected 250-pct 
increase in service life should more than 
offset the battery's higher initial cost. 



INT.-BU.OF MINES, PGH., PA. 26925 



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